The purpose of this study is to determine the efficacy of a behavioral intervention to reduce high&#8209;risk transmission behaviors among hepatitis C virus (HCV)&#8209;infected young injection drug users (IDUs), and to identify the proportion that would be eligible and willing to undergo treatment to eradicate HCV infection. Since 65&#8209;95% of IDUs are HCV seropositive, untreated, and capable of transmitting infection, a very large reservoir of HCV infection exists. HCV is often the first blood borne infection to be acquired among new IDUs; therefore, HCV prevention strategies are relevant to HIV prevention. Under a separately funded multi&#8209;site study of young and new injectors, we have developed a peer&#8209;based HCV education intervention and are engaged in a study to evaluate its efficacy in reducing behaviors that may lead to HCV and HIV infection among HCV&#8209;negative young IDUs. We propose to test the ability of an intervention based on the same behavioral theory to reduce risk behaviors among young HCV&#8209;seropositive IDUs. Our specific aims are: 1) To determine the efficacy of a "peer&#8209;volunteer activism" intervention to reduce high&#8209;risk transmission behaviors among 750 HCV&#8209;infected young IDUs in three US cities, when compared to an attention control condition at 3, 6 and 12&#8209;month post-intervention; 2) To measure the proportion of HCV seropositive IDUs who are eligible for HCV therapy according to four broad criteria: i) evidence of active infection or liver disease, as indicated by serum ALT levels and HCV&#8209;RNA, ii) pre&#8209;existing conditions that may be contraindications for treatment, including depression and alcohol use, iii) potential for re&#8209;infection via continued unsafe injection drug use, and iv) completion of medical screening visits, as an indicator of readiness for HCV therapy; 3) To develop and validate an instrument to identify individuals who demonstrate a readiness to undergo HCV therapy. To meet these aims, we will recruit, screen, and randomly assign 750 young HCV&#8209;antibody positive IDUs in Baltimore, New York and Seattle to a behavioral intervention, and prospectively monitor participants quarterly for 12 months. The primary outcome for Aim 1 is to reduce distributive needle sharing; secondary outcomes include alcohol use, sharing of other injection paraphernalia, HIV infection, and increase condom use. Through Aim 2, we will compare the proportion of IDUs who meet current and new consensus guidelines for HCV therapy, revisions for which are scheduled for 2002. Through Aim 3, we will develop a tool to assess HCV treatment readiness with broad applications for clinical decision-making. By addressing both behavioral and clinical research questions, this project will help lessen the burden of HCV and HIV infection in this high&#8209;risk population and will serve to inform policy decisions, including revised clinical guidelines for HCV treatment.